What is the formula for available carbohydrates?

November 2, 2025 •

3 min read

According to the Food and Agriculture Organization of the United Nations, a carbohydrate's small-intestinal digestibility is its most important nutritional property. The formula for available carbohydrates is critical for understanding this, as it distinguishes between digestible carbs that provide energy and indigestible dietary fiber.

Quick Summary

This article explores the formulas for calculating available carbohydrates, detailing the two primary methods: the summation of individual digestible components and the 'by difference' calculation. It explains the crucial distinction between available carbohydrates and total carbohydrates, including the role of dietary fiber, and discusses how food labeling regulations differ globally.

Key Points

Two Primary Formulas: Available carbohydrates can be calculated by either directly summing up digestible components (sugars, starches) or by subtracting dietary fiber and other non-digestible elements from total carbohydrates.
Available vs. Total Carbs: The key difference lies in dietary fiber; available carbohydrates exclude it, while total carbohydrates include it.
Food Labeling Varies: Depending on the country, food labels may display available carbs (EU) or total carbs (USA), requiring consumers to adjust calculations.
Health Relevance: Knowing available carbohydrates is crucial for managing blood glucose levels, especially for people with diabetes.
Net Carbs: The term 'net carbs' is equivalent to available carbohydrates, representing the carbs that are absorbed and affect blood sugar.
Method Accuracy: The summation method is more precise for specific nutrients, whereas the 'by difference' method can accumulate measurement errors.

Understanding the Formula for Available Carbohydrates

Available carbohydrates are the portion of total carbohydrates that can be digested and absorbed by the human body to be used for energy. This value is distinct from total carbohydrates and is important for nutritional analysis, particularly for those managing blood sugar levels. There are two main methods to calculate available carbohydrates: the direct summation method and the 'by difference' method.

The Summation Method: A Direct Approach

The summation method is considered precise as it involves directly measuring and adding up the specific digestible carbohydrate components in food. This is often used for novel foods or specific nutritional claims. The formula involves summing the carbohydrate types that the body can metabolize, such as:

Available Carbohydrates = (Total Sugars + Starch + Glycogen + Available Oligosaccharides + Dextrins + Maltodextrins)

This method excludes indigestible fiber, focusing on carbs that impact blood sugar. Some regulations may include sugar alcohols in this calculation.

The 'By Difference' Method: An Indirect Calculation

The 'by difference' method is a less direct approach, often found in older data and some regulations. It calculates total carbohydrates by subtracting the weight of moisture, protein, fat, and ash from the total food weight. Available carbohydrates are then found by subtracting dietary fiber from this total carbohydrate figure. The steps are:

Step 1 (Total Carbohydrates): Total Carbohydrates = Total Weight of Food - (Moisture + Protein + Fat + Ash)
Step 2 (Available Carbohydrates): Available Carbohydrates = Total Carbohydrates - Dietary Fiber

This method can be less accurate due to the accumulation of errors from measuring other components.

Available Carbohydrates vs. Total Carbohydrates

The difference between available and total carbohydrates is a key factor in understanding food labels globally.

Total Carbohydrates: This includes all carbohydrates, both digestible and indigestible (like fiber). On US Nutrition Facts labels, this is the main 'Carbohydrates' listing.

Available Carbohydrates (or 'Net Carbs'): This figure excludes dietary fiber, representing only the carbohydrates that are converted to glucose. This is important for those on low-carb diets or managing diabetes. EU food labels effectively show available carbohydrates by listing 'Carbohydrate (of which sugars)' and 'Fibre' separately.


Feature	Total Carbohydrates	Available Carbohydrates
Definition	Includes all carbs: sugars, starch, and fiber.	Includes only digestible carbs: sugars and starch.
Energy Contribution	Provides energy from starches and sugars; fiber contributes very little, if any.	Directly contributes to the body's energy supply.
Impact on Blood Sugar	Less direct, as fiber moderates the blood sugar response.	Direct and more immediate impact on blood sugar levels.
Used in Labeling	Used in the USA; often requires manual subtraction for 'net carbs'.	Used in the EU and other regions; can be explicitly listed or derived from the label.
Calculation Method	Often calculated 'by difference' in a lab setting.	Can be calculated by summation or by subtracting fiber from total carbs.

Global Variations in Food Labeling

Food labeling varies internationally, impacting how carbohydrate information is presented.

United States: Labels show "Total Carbohydrates" and a separate "Dietary Fiber" line. Consumers calculate available carbohydrates (or "net carbs") by subtracting fiber from total carbs.
European Union: Labels list "Carbohydrate" and "Fibre" separately. The "Carbohydrate" value essentially represents available carbohydrates as it excludes fiber.
Australia/New Zealand: Similar to the EU, labels report available carbohydrates, not including dietary fiber.

Conclusion: The Importance of Accurate Carbohydrate Calculation

Understanding the formula for available carbohydrates is vital for manufacturers and consumers. It helps distinguish between energy-providing carbs and non-digestible fiber. While manufacturers may use precise methods like summation, consumers can estimate available carbohydrates from labels by subtracting fiber from total carbs, keeping regional variations in mind. This knowledge supports informed dietary choices, particularly for managing health goals like blood sugar control.

List of Common Digestible Carbohydrates

Monosaccharides: Simple sugars like glucose, fructose, and galactose.
Disaccharides: Sugars like sucrose, lactose, and maltose.
Polysaccharides: Complex carbs including starches and glycogen.
Dextrins: Carbohydrates from starch or glycogen hydrolysis.
Maltodextrins: Starch-derived polysaccharides used as additives.

Key Formulas for Available Carbohydrates

Available Carbohydrates (by subtraction) = Total Carbohydrates - Dietary Fiber

Available Carbohydrates (by summation) = Sugars + Starches + Other Available Carbohydrates

Accurate calculation is crucial for nutritional planning. For more detailed information, consult resources like USDA FoodData Central and Food Standards Australia New Zealand.

Frequently Asked Questions

The simplest method for a consumer is to look at the food's nutrition label and subtract the grams of dietary fiber from the grams of total carbohydrates listed.

Differences in food science and regulatory standards between countries like the US and EU lead to different labeling conventions. The EU favors showing available carbs, while the US includes fiber in the total carbohydrate count.

Dietary fiber is generally not digestible by the human body and therefore provides very little, if any, calories. Some fiber is fermented by gut bacteria, which can provide a small number of calories, but this is usually not included in standard available carbohydrate calculations.

Some available carbohydrate calculations, particularly in specific food standards, may include sugar alcohols, while others do not. Their impact can also vary, and in some cases, they are subtracted along with fiber.

This refers to a laboratory method where carbohydrates are not measured directly. Instead, all other components (moisture, protein, fat, and ash) are subtracted from the total weight of the food, with the remainder being attributed to total carbohydrates.

Available carbohydrates are the portion that is digested and converted into glucose, directly impacting blood sugar levels. Dietary fiber is not absorbed and thus does not cause a blood sugar spike.

Yes, for the purpose of nutrition tracking and health management, 'net carbs' is generally considered a synonym for available carbohydrates, representing the amount of carbs that the body will actually use for energy.